The widely practiced art of screen printing generally involves the application of inks through taughtly stretched screens or meshes. For this purpose, a screen is typically stretched over, and fixed on, a rectangular (sometimes square) frame. There are two general types of frames which have gained common acceptance in the trade. First, there are frames designed for a single use. These frames are often made of wood. The screen is usually glued to the wood after being stretched over the frame. Second, there are frames which are designed for repeated use. These frames are often referred to as "roller frames". Each of at least three sides (usually four sides) of a roller frame typically includes a cylindrical roller, a groove running substantially along the length of the roller, a bolt-like end portion which can be torqued by a wrench, and a locking mechanism for controlling the rotational freedom of the roller. One such roller frame is referred to as a Newman Roller.TM., and is sold by Stretch Devices of Philadelphia. Another such roller frame is sold by Diamond Chase Company, Inc. of Huntington Beach, Calif. The present invention involves the second-mentioned type of frame, i.e., reusable roller frames.
Up until now, the conventional method of stretching a screen on a roller frame is a manual process requiring the following steps: (1) the screen is placed in the frame and secured to the frame by urging the mesh into the roller grooves, then inserting a dowel or flexible strip into each of the grooves; (2) the frame is placed on a table with the screen side down; (3) a wrench is applied to a bolt-like end portion of one of the sides of the frame, and torqued, thus stretching the screen; (4) a jam bolt is tightened to prevent the roller from further turning; (5) steps 3 and 4 are repeated sequentially for each of the other sides of the frame; and (6) the frame is then turned over and the tension of the screen is tested. This process is typically repeated two to five times before the proper tension for the screen is achieved. This manual process of stretching a screen on a roller frame usually takes between 5 and 45 minutes, depending on the skill of the operator.
There are at least four significant problems and/or limitations with the use of roller frames and manually stretched screens. First, the period of time required to manually stretch a screen on a roller frame (5-45 minutes) is considered by many in the industry, to be too long to make the use of roller frames cost effective. Second, a flat frame is hard to achieve and/or maintain with the manual stretching process. However, frame flatness is critical for proper printing registration. Third, with the manual process, it is difficult to achieve the proper tension in both directions (weft and warp). However, it is critical for precision printing, that the screen be stretched to the proper tension in both directions. Fourth, the ability to manually stretch the screen on a roller frame is highly dependent on the skill and experience level of the operator.
Accordingly, a primary objective of the present invention, is to provide a more rapid way of stretching a screen on a roller frame. Another object of the invention is to provide a method of stretching a screen on a roller frame which is not appreciably dependent on the manual skill of the operator. Still another object of the invention is to provide a device which is capable of stretching a screen, with proper tension in both directions, and on a roller frame which remains flat.